4. HANG GLIDING
The problem we now consider is to compute the flight inputs to a hang glider so as to
provide a maximum range flight. The specific problem we shall analyze is taken from [7].
One should note that the model presented here also applies to the flight of an airplane
with its engines off (only the data are different). In this case, maximizing the range could
be a life-saving endeavor.
The hang glider (with pilot) is pulled down by the force of gravity associated with its
mass m, has a lifting force L acting perpendicular to its velocity relative to the air, and
TRAINS, PLANES, AND OTHER PASTIMES 19
a drag force D acting in a direction opposite to the relative velocity. Denote by x the
horizontal position of the glider, by vx the horizontal component of the absolute velocity,
by y the vertical position, and by vy the vertical component of absolute velocity.
Recall that one of the lessons of the previous section is the importance of scrutinizing
every model carefully looking for errors. With that in mind and with our apologies for not
practicing what we preach, we ask the reader to trust us as we assert that the following
description of the equations of motion for a hang glider is correct.